Process of extruding steel



the stress-strain curve' where Un ed ws, am

PROCESS OF EXTRUDING STEEL Elliot S. Nachtman, Park Forest, and Eldon B. Moore, Calumet City, 11]., assignors to La Salle Steel Company, Hammond, Ind., a corporation of Delaware 1 'No Drawing. Application June 27, 1955,

Serial No. 518,414 I 13 Claims (Cl. 207-) This invention relates to .an improved metallurgical process for use in the treatment of strain hardenable steels which also harden by precipitation to develop mechanical properties inthe steel 1 which, in some cases, exceed and in other cases are equivalent to those produced by cold working or vcold working followed by stress relief.

i ,This application is a'continuation-in-part of our co- I the steels of the 450 F. but below the lower particular steel composition, such as at a temperature be- 2,767,838 Patented Oct. 23 1956 the material is capable of sustaining without deviation from the law of proportionality of stress to strain occurs ('Hookes law). This point is of particular importance in steel and, in particularly every instance, is measurably increased to heretofore unobtainablehigh values when non-austenitic type are produced, as by drawing or extrusion, at elevated temperatures within the range defined in the aforementioned copending applications.

In said copending applications, description is made of a new and improved metallurgical process wherein properties heretofore secured only by taking abnormally heavy drafts and stress relieving, such as described in the Landis Patent No. 2,320,040, wherein description is made of a process for cold finishing of steel as *by drawing to produce a smooth and satisfactory surface finish are capable of being, equalled and, in most instances, surpassed by a more simplifiedand more economical process embodying the features of this invention .wherein the steel is heated for drawing to a temperature above critical temperature for the low MOO- 1200" F. 'For the particular properties which it is desired to develop in the steel in accordance with the practice of this invention, it is preferred to work the steel as by drawing within the temperature range of above 450 F. up to about 600 F. {It has been found that byreason of the reaction which takes place upon Working of the steel at the elev'ted temperature and under the pressure conditions existing during passage through the die, development of the described improvesteel while concurrently incorporating improved mechanical properties such as are incapable of being produced by processes heretofore employed, particularly with respect to such properties as tensile strength, proportional limits, and hardness with and without noticeable affect on the ductility of the steel, thereby to achieve the production of a new and improved steel of the type described.

A further object is to provide a metallurgical process for producing steels embodying characteristics of the type described by the simple medium of working the steel as by drawing or extrusion without noticeable increase in warping value and more particularly with reduced residual stresses and stress control without the necessity for additional steps heretofore employed for stress relieving drawn steel.

i As used herein, the term machinability is intended to define the ability of the metal to be cut, ground or processed by machine tools normally used in the fabrication of steel products. Machin'ability characteristics, as defined herein, are evaluated by comparison of the steel as against a standard specimen mountedon a lathe and cut with a non-driven tool. Constant pressure is asserted on the lathe tool as it cuts. This constant pressure of the cutting tool causes widely varying feeds depending upon the machinability of the metal being tested and, when everything else is held constant, the feed rate may be taken as a measurement of the macbinability of the steel.

The physical property of surface roughness constitutes a measurement taken by means of a profilometer which measures the surface of the roughness in terms of microinches.

As used herein, the term mechanical properties is intended to include such properties as tensile strength, yield strength, proportional limit, impact strength, and hardness.

w The term proportional limit corresponds to the point ments in physical and mechanical properties are secured in combination with improvement in the machinability of the steel. 7 i

As to the mechanical properties, it has been found that by drawing at elevated temperatures within the range defined, it is possible by taking normal drafts to achieve strength properties, proportional limits and hardness comparable to those secured by the aforementioned Landis patent, without subsequent furnacetreatment or strain relieving. At abnormally heavy drafts, with steel heated to elevated temperatures, in accordance with the practice of this invention, mechanical properties are'embodied in the steel product whichexceed the values secured in steels processed inaccordance with the teaching of the Landis patent. Such unexpectedly high'values, which are secured, make it possible to substitute readily available and low cost non-austenitic steels for the more expensive heat treated steels or for the more costly and less available alloy steels.

In contrast to the multiple steps heretofore employed in prior art processes, mechanical properties far superior to those secured by such multiple operations can be secured, in accordance with the practice of this invention,

' in a single operational step simply by drawing the steel under controlled temperature conditions whereby, in addition to the improvement of mechanical properties, the drawn steel products are characterized 'by less warpage when drawn at the appropriate temperatures.

It has also been found that by proper control of temperature and draft, new and unexpected proportional limits and yield strengths are capable of being developed in steels of the non-austenitic type having a pearlitic structure in a matrix of free ferrite. As would be expected, proportional limits and yield strengths parallel each other in many respects It has been found thatby heating the steel to a temperature Within the range of greater than 450 F. to 850 F.. and preferably above 450 F. to 600 F., superior results are. secured both in proportional limits and yield strengths' The development in such unexpected properties and yield strengths and-proportional limits is dependent somewhat on the amount of draft, the temperature at which the optimum properties are secured and the chemistry of the steel.

The process to improve the physical and mechanical properties of steels of the type described, such as are secured by working as by drawing or extrusion of the steels at elevated temperatures within the range described, can advantageously be further divided depending upon the elastic properties desired in the end product. It has been found further that it is possible to control precipitation hardening to any desired extent where one has available the desirable amount of work hardening and precipitation hardening. When the steel is worked, as by drawing or extrusion, to effect reduction in cross-sectional area while the steel is at a temperature of 600 F. or above,

the elastic properties of the steel produced is improved. Processing the steel at a temperature below 600 F. but above 450' F., in accordance with the practice of this invention, results in decreasing the elastic properties of the steel. In other words, ductility of the steel produced or its, measurable elastic properties are minimized while still achieving the other desired improvements in machinability and mechanical and physical properties when the, steel is drawn at a temperature above 450 F. but below 600 F.

This may be illustrated by the data which will hereinafter he set forth. The property of elongation, which will be referred to in the data, illustrates the ductility or the elastic properties of the steel. Thus for steels having improved ductility coupled with other improvements in mechanical and physical properties, it is desirable to work the steel, as by drawing, at a temperature within the range of 600-850" F. When it is desirable to produce steels for various uses having high strength properties but with lesser ductility, it is preferred to process the steel, as by drawing or extrusion to effect reduction in cross-sectional area, while at a temperature below 600 F. but preferably above 450 F., as described and claimed herein.

As previously pointed out, machinability of the steels may also be improved by processing the steels in the manner described for improvement of the mechanical and physical properties. Some of the non-austenitic steels appear to be substantially insensitive to the temperature of drawing as regards their machinability characteristics, but important improvements in machinability may be caused to result in steels of other chemistries when drawing is effected within a well defined temperature range thereby further to improve the metallurgical treatment of steels to make them more readily adaptable for subsequent use.

From the practical standpoint, it is known that for some grades of non-austenitic steel having more than 0.10 percent carbon but less than 0.65 and preferably less than 0.5 percent carbon, the machinability of the steel is increased by drawing at a temperature within the range of over 450 F. to about 850 F. Within this range, very important and marked improvements in machinability result in non-resulphurized low sulphur steels having a carbon content between 0.10 and 0.35 percent by weight.

Typical of the steels in which the improvements in physical and mechanical properties are capable of being developed in the manner herein described are steels which can be strain hardened and which harden by some mode of precipitation at temperatures below the lower critical temperature. If the steel shows hardening because of precipitation or other re-arrangement, then it becomes possible to improve the strength properties and the physical properties of the steel by the practice of this inventionwherein the steel is drawn at elevated temperatures to etfect reduction in cross-sectional area.

Representative of such steels, which exhibit the desired characteristics for use in the practice of this invention, are the non-austenitic steels having a pearlitic structure: in a matrix of free ferrite, including plain carbon 4 steels, and low alloy, low and medium carbon steels. In steels having little or no free ferrite in their structures, machinability appears to be substantially unaffected by temperature of drawing. On the other hand, nonaustenitic steels containing substantial amounts of free ferrite hardened during the drawing operation exhibit marked improvements in machinability by proper control of the temperature of drawing to above 450 F. but below 850 F., particularly in non-austenitic steels having a carbon content between 0.10 and 0.25 percent.

While the improvements in machinability depend somewhat upon the chemistry of the steel, the amount of draft and the temperature conditions existing during the drawing operation, surface roughness appears not to be so dependent, although surface. roughness is vastly improved by working the steel at elevated temperatures.

The following example will illustrate the concepts of this invention as related to the property of machinability in which the steel compositions are defined by the major ingredients other than iron.

EXAMPLE 1 In one series of tests, hot rolled Bessemer screw stock steel, a free machining grade of the non-austenitic type having a pearlitic structure in a matrix of free ferrite, was drawn at various temperatures to achieve a 19 percent reduction from inch rounds. The composition of the steel is as follows:

0.08 percent carbon 0.75 percent manganese 0.12 percent phosphorus 0.27 percent sulphur 0.01 percent silicon 0.015 percent nitrogen EXAMPLE 2 In another series of tests, hot rolled open hearth medium medium carbon steel of fair machinability of the non-austenitic type having a pearlitic structure in a matrix of free ferrite was drawn at temperatures corresponding to that in Example 1 to achieve a similar reduction from inch rounds. The composition of this steel is as follows:

0.48 percent carbon 1.50 percent manganese 0.03 percent phosphorus 0.27 percent sulphur 0.30 percent silicon 0.005 percent nitrogen EXAMPLE 3 In a third series of tests, hot rolled open hearth low sulphur steel of relatively poor machinability of the nonaustenitic type was drawn under the conditions of Examples l and 2 to achieve a similar reduction from inch rounds. The composition of this steel is as follows:

0.17 percent carbon 0.75 percent manganese 0.03 percent phosphorus 0.04 percent sulphur 0.08 percent silicon 0.005 percent nitrogen Procedure -Bars of each of the compositions above were passed. through the drawing die with the usual lubricants 0n the surfaces thereof without any previous heating. Other bars of each composition were heated to various temperature levels and then passed through the same die with the same type of lubricant on the surfaces thereof to achieve a 19. percent reduction in cross-sectional area. The drawn bars were allowed to cool naturally to room condition and then tested for machinability. The following; table. sets forth, the. results secured.

Table I .Cmparis0rt of machinability with various steels drawn at various temperatures Maehlnability rating in percent based on B1112 as IOOpercent Temp. of Steel drawn (F.)

Steel of Steel of Steel of Example 1 Example 2 Example 3 It Wlll be apparent from the results that the Bessemer steel composition of Example 1, characterized by a carbon content of less than 0.10 percent and a relatively high phosphorus and sulphur content, enjoys high machinability which is not profoundly influenced by this process. On the other hand, the composition of the open hearth low phosphorus and low sulphur steel of Example 3, having a carbon content of 0.10 percent, depends upon a predetermined balance of temperature, draft and chemistry to secure marked improvements in machinability. When drawing steel of the types of composition 3 at a temperature between 75450 F., machinability ratings of only 53 are obtained. However, in accordance with the practice of this invention, when the'same steel is drawn at temperatures within the range defined herein, the machinability rating of the drawn steel is increased markedly to a value of about 62. Such improvement in machinability at temperatures within the range of 450-850 F. constitutes a very important factor with respect to the wider application of such steel and the ability to machine the new high strength steel. It also is reflected in marked savings in scrap or loss of parts due to breakage, cracking or failure. The chemistry of the steel of Example 2, which is a medium carbon high sulphur steel, is such as to provide for some improvement in machinability at temperatures within the range of 450-850 F. When the steels of Examples 2 and 3 are heated to temperatures in excess of 840 F. for drawing, the machinability drops significantly and renders metallurgical treatment of such temperature ranges impractical where machinability might be of importance. j The following examples will illustrate the improvements which are secured in the hardness and in the proportional limits of steels embodying the features of this invention:

EXAMPLE 4 Steel composition:

0.08 percent carbon 0.75 percent 0.12 percent 0.27 percent 0.01 percent 0.015 percent Steel composition: v0.17 percent 0.75 percent 0.03 percent 0.04 percent 0.08 percent 0.005 percent.

Steel composition:

0.48 percent 1.50 percent -j-' 0.03 percent 0.27 percent 'f0.30 percent a l oitq ent manganese phosphorus sulphur silicon nitrogen EXAMPLE Procedure.'Steel bars of the above compositions pre duced by conventional hot rolling practice so-that they have a normal pearlitic and ferritic structure were advanced through a drawing die to achieve a 19 percent reduction in cross-sectional area from bars of inch round. One set of bars were drawn with lubricant on the surface but without any previous heating to elevated temperature. Other bars were drawn through the same die with the same lubricant but heated for drawing to various elevated temperatures ranging up to about 1050 F. Hardness and proportional limits were determined for each and the values are listed in the following table for purposes of illustrating the eifect of temperature corn trol and chemistry on the development of such physical properties in steels ot the types descrlbed.

Table II Proportional Surface Brinell Hardness limits Roughness Temp. of (1,000 p. s..i.) (micro-inches) steel drawn (F.) Steel Steel Steel Steel Steel Steel Steel Steel Steel of of of of of Ex.4 Ex.5 Ex.6 Ex.4 Ex.5 Ex.6 Ex.4 Ex.5 Ex.6

It will be observed from the above that with bars drawn to a 19 percent reduction in cross-sectional area within the temperature range of 450750 F., the hardness and proportional limits'are at considerably higher values than those which are secured at temperatures below and above the described range.

The improvements in the mechanical and physicalproperties and the improvement in ductility of the steel when drawn at a temperature above 450 F. concurrently with the improvements in mechanical and physical properties can be illustrated by the following tables with non-austenitic steels of the type described including low alloy steels.

EXAMPLE 7 Steel composition: 0.16 percent carbon 0.71 percent manganese 0.01 percent phosphorus 0.03 percent sulphur 0.25 percent silicon 0.005 percent nitrogen Pr0c,edure.-Bars of the above steel composition were given a 5 percent reduction by drawing A; inch bars to approximately inch or about a 2 inch draft at various temperatures ranging fromroom temperature up to about 900 F. Another set of bars A; inch in diameter were given a 30 percent reduction by drawing to about inch or nearly a inch draft at the various temperatures. Drawing was effected at a speed of about 10 feet per minute using a lubricant such as Sinclair Oil Company No. L571.

Table III.5 percent reduction Tensile Yield Elong. Warpage strength, strength, 1%", Factor p. s. i. p. s. i. percent Hot Rolled Material 66, 000 50, 000 36 056 Temp. of Draw, F.:

Table lV.-30 percent reduction T able. VIII.-30 percent reduction Tensile Yield Elong. Warpage Tensile Yield Eloug. Warpstrength, strength, 1%", Factor Strength, Strength, 1%", age

p. s. i. p. s. 1. percent 5 p. s. i. p. s. i. Pcrcen Factor Hot Rolled Material... 00, 000 50, 000 so +.05e Hot Rolled Material... 140, 250 102,000 17. 5 016 Temp. of Drew, F.: Temp. t Draw, F.:

EXAMPLE 1O EXAMPLE 8 1 Steel composition: Steel composition: 63 steam Garb n 0.44 percent carbon p ercent anese 1.52 percent manganese ercem hows 0.18 percent phosphorus gercent g g 0.31 ercent su hur P 1p 20 .29 percent s1l1con 0.25 percent silicon 0.005 percent nitrogen Pr0cedure.The same procedure was followed for testing as in Example 7.

Table V.5 percent reducnon Tensile Yield Elong. Warpagc strength, strength, 1%", Factor p. s. i. p. s. i. percent Hot Rolled Material..-" 113, 500 76, 250 23 032 Temp. 01 Draw, F.:

Table Vl.30 percent reduction Tensile Yield Elong. Warpage strength, strength, 1%", Factor p. s. i. p. s. i. percent Hot Rolled Material"... 113, 500 75, 250 23 032 Temp. 01 Draw, F.

EXAMPLE 9 Steel composition:

Pr0cedure.-The low alloy steel of the above composition was processed for testing as described in Example 7.

Table VII.-5 percent reduction .83 percent chromium Procedure-The same procedure was followed for testing as in Example 7 except that the amounts of reductions were 6.7 percent and 25 percent.

Table IX.6.7 percent reduction Tensile Yield Elong. Warpage strength, strength, 2, Factor p. s. i. p. s. i. percent Hot Rolled Material..- 146, 750 89, 500 13 +1128 Temp. olDraw, F.:

Table X .25 percent reductmn Tensile Yield Elong. Warpage strength, strength, 2", Factor p. s. i. p. s. i. percent 1 Hot- Rolled Material".-- 146, 750 89, 590 13 028 Temp. 01 Draw, F.:

EXAMPLE 1 1 Table XI .--1 0 percent reduction Tensile Yield Elong. Warpage Tensile Yield Elong. Wei-page strength, strength, 1%", Factor strength, strength, 2", Factor p. s. i. p. s. 1. percent p. s. i. p. s. 1. percent Hot Rolled Material..." 140, 250 102,000 17. 5 016 Hot Rolled Material. 124,330 110,800 16 --,u)

Table XIl. 35 percent reduction vEXAMPLE 12 Steel composition:

.41 percent carbon 6 .81 perc ent .;manganese V .012 percent phosphorus .033 percent sulphur .26 percent silicon .30 percent nickel .20 percent chromium .10 percent molybdenum .0008 percent beryllium.

Procedure-The same procedurewas followed for testing as in Example. 7 except that reductions of 6.7 and 25 percent were taken.

Table XIII.- 6.7;percent reduction Tensile Yield Elong. Warpage strength, strength, 2", Factor p. s. i.'. p. s. i. percent Hot Rolled Material 125, 500' 82,500 V 20 048 Temp. of Draw, F.. v

' 140 125, 750 120, 000 14 216 360--. 125, 625 116, 250 14 198 420--. 128,250 115,000 13 170 480. 151, 500 151, 500 7 169 520. 151,000 151,000 V 9' 140 I. 585 152, 500 .152, 000' a 10 142 630. 139,000 135, 000 13 156 685. 143,250 130,000 13 +.'142

Table XI V.25 percent reductzon Tensile Yield Elong. Warpage strength, strength, 2", Factor p. s. i. 1).8. i. percent It be'observedfrom the foregoing tables that the tensile -'str'engths"and yield strengths are markedlyincreasedby drawing steels of the type described to effect r'dubtio'n'in cross-sectional area' while the steelsare heated to a temperature above 450 F. to about 850- F. It will be observed also that at temperatures below 600 F. the percent elongation of the steels decreases, indicating a decrease in the elastic properties whereas the percent elongation begins to increase materially when the steel is drawn above 600 F. Thus steels are produced having improved physical properties and mechanical properties concurrently with minimized elasticity and steels may be produced for other purposes having similarly improved physical and mechanical properties concurrently with improved elasticity merely by the proper selection of the temperature for drawing the steel.

The method of heating the steel to the desired temperature of drawing is unimportant. Heating may be achieved by any number of ways well known in the art, such as by an electric furnace, resistance heating or the like. For example, the steel may be heated by means of a saltlbath which may advantageously be used also to coat the metal with a. lubricant and otherwise condition the pending application of Nachtman, Serial No. 286,039,

filed May 3, 1952, wherein description is made that, in the past, the metal hasbeen prepared for deformation to produce a better finish in a cold finishing operation by treating the surface of the metal first with an acid to remove scale, followed by a rinse to remove acid, followed further by liming to protect the surface and to prepare the surface for subsequent application of lubri cant prior to cold working or drawing. The improvement described in the aforementioned copending application resides in the development of a process wherein-the various steps of descaling, washing, liming and lubricating are provided in a single step wherein the steel "is treated with a molten bath of sodium hydroxide and-a reducing agent wherein the steel is descaled by chemical reduction and wherein the steel is heated to thedesired temperature for advancing the steel through the die to effect reduction in cross-sectional area in accordance with the practice of this invention. Instead of applying molten salts for purposes of lubrication, use may be made of conventional lubricating compounds. 1

From the foregoing it will be apparent that anew and simplified metallurgical process has been developed for the production of steels having controlled warpage values, having improved machinability, improved surface characteristics and markedly increased strength properties; The development of steels having such tailor-made characteristics may be produced by the proper selection of chemistry, draft and temperature in a single operation thereby to produce steels incapable of being secured by processes heretofore employed other than by the use of multiple steps of working followed by heat treatmentor strain relieving or by the use of more expensive and'less available alloy steels. 'These other steels, in most instances, are incapable of having incorporated therein the various combinations of physical and mechanical properties which can be introduced into steel products by the simple metallurgical process herein described and claimed.

It will be understood that changes may be made in the details of processing and in the manner of heating and cooling of the steel during working as by drawing or extrusion without departing from the spirit of the/invention, especially as defined in the following claims.

We claim:

1. The metallurgical process for the improvement of mechanical and physical properties of a hot rolled steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite and which strain hardens and hardens by some mode of precipitation when worked at 'a temperature between 450600 F., comprising the steps of descaling and lubricating the surfaces of the steel and drawing the hot rolled steel through a drawing die to effect reduction in cross-sectional area while the steel is heated to a temperature above 450 F. but below 600 F. whereby physical and mechanical properties of'the steel are improved.

2. The metallurgical process comprising the steps of descaling the steel and lubricating the surfaces of the steel and drawing a hot rolled steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite and which strain hardens and hardens by some mode of precipitation when worked at a temperature between 450600 F. and which has a carbon content up to 0.65 percent by Weight to effect reduction in crosssectional area while the steel is at a temperature above 450 F. but below 600 F. whereby the drawn steel is characterized by improvements in tensile strength, yield strength, hardness and proportional limits.

3. The metallurgical process for the improvement of mechanical and physical properties of a hot rolled steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite and which strain hardens and hardens by some mode of precipitation when worked at II a temperature between 450600 F., comprising the steps of descaling and lubricating the surfaces of the steel and extruding the steel through a die to effect reduction in cross-sectional area while the steel is heated to a temperature above 450 F. but below 600 F. whereby physical and mechanical properties of the steel are improved.

4. The metallurgical process comprising the steps of descaling the steel and lubricating the surfaces of the steel and extruding a hot rolled steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite and which strain hardens and hardens by some mode of precipitation when worked at a temperature between 450-600 F. and which has a carbon content up to 0.65- percent by weight to effect reduction in cross sectional area while the steel is at a temperature above 450 F. but below 60 F. whereby the extruded steel is characterized by improvements in tensile strength, yield strength, hardness and proportional limits.

The metallurgical process comprising the steps of descaling the steel and lubricating the surfaces of the steel and drawing hot rolled steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite and which strain hardens and hardens by some mode of precipitation when worked at a temperature between 450-600 F. and which has a carbon content within the range of 0.10 to 0.65 percent to effect reduction in crosssectional area while the steel is at a temperature above 450 F. but below 600 F. whereby the steel is characterized by new and improved machinability properties.

6. The metallurgical process for the improvement of mechanical and physical properties and machining characteristics of hot rolled steel which strain hardens and hardens by some mode of precipitation during working at a temperature within the range of 450600 F. comprising the steps of descaling the steel and lubricating the surfaces of the steel and drawing a hot rolled steel of the non-austenitic type having a pearlitic structure in a matrix of free ferrite and having a carbon content within the range of 0.1 to 0.35 percent to effect reduction in crosssectional area while the steel is at a temperature above 450 F. but below 600 F.

7. The metallurgical process for the improvement of mechanical and physical properties of hot rolled steel which strain hardens and hardens by some mode of precipitation when worked at a temperature of 450600 F., comprising the steps of descaling the steel and lubricating the surfaces of the steel and drawing the hot rolled steel through a draw die to effect reduction in cross-sectional area while the steel is at a temperature above 450 F. but below 600 F.

8. The metallurgical process for the improvement of mechanical and physical properties of a hot rolled steel which strain hardens and hardens by some mode of precipitation when worked at a temperature of 450600 F., comprising the steps of descaling the steel and lubricating the surfaces of the steel and extruding the hot rolled steel through a die to effect reduction in cross-sectional area while the steel is at a temperature above 450 F. but below 600 F.

9. The metallurgical process for the improvement of mechanical and physical properties of hot rolled steel in which tensile strength, yield strength, proportional limits, hardness, and machinability are maximized, and in which the steel is charcterized' by being capable of strain hardening and which hardens by some mode of precipitation upon working at a temperature below the lower critical temperature for the steel composition, com prising the steps of descaling the steel and lubricating the surfaces of the steel and advancing the steel through a die to effect reduction in cross-sectional area while the steel is at a temperature above 450' F. but below 600 F.

10. A steel product having improved mechinability in combination with improved mechanical and physical properties produced by the method of claim 9.

11. The metallurgical process for improving the machinability of hot rolled steel and for the improvement of mechanical and physical properties of the steel in which the steel has a carbon content. within the range of 0.1 to 0.5 percent and wherein the steelstrain hardens and hardens by some mode of precipitation during working at a temperature within the range of 450-600" F. for the steel composition, comprising thesteps of descaling the steel and lubricating the surfaces of the steel and advancing the steel through a die to. efiect reduction in cross-sectional area while the steel is at a temperature above 450 F. but below 600 F.

12. In a metallurgical process for producing the properties of cold finished, hot rolled steel bars having improved mechanical and physical properties while maintaining ductility and wherein the hot rolled steel bars strain harden and harden by some mode of precipitation when worked at a temperature within the range of 450-600" F., the steps of descaling the steel bars and lubricating the surfaces of the steel bars, and advancing the steel bars through a die to etfect reduction in crosssectional area while the steel is at a temperature above 450 F. but below 600 F.

13. In a metallurgical process for producing the properties of cold finished, hot rolled steel bars having improved mechanical and physical properties while maintaining ductility and wherein the hot rolled steel bars strain harden and harden by some mode of precipitation when worked at a temperature within the range of 450-600 F., the steps of descaling the steel bars and lubricating the surfaces of the steel bars, and drawing the steel bars through a draw die to effect reduction in crosssectional area while the steel is at a temperature above 450 F. but below 600 F.

References Cited in the tile of this patent UNITED STATES. PATENTS Buchholtz May 8, 1934 OTHER REFERENCES 

1. THE METALLURGICAL PROCESS FOR THE IMPROVEMENT OF MECHANICAL AND PHYSICAL PROPERTIES OF A HOT ROLLED STEEL OF THE NON-AUSTENITIC TYPE HAVING A PEARLITIC STRUCTURE IN A MATRIX OF FREE FERRITE AND WHICH STRAIN HARDENS AND HARDENS BY SOME MODE OF PRECIPITATION WHEN WORKED AT A TEMPERATURE BETWEEN 450-600* F., COMPRISING THE STEPS OF DESCALING AND LUBRICATING THE SURFACES OF THE STEEL AND DRAWING THE HOT ROLLED STEEL THROUGH A DRAWING DIE TO EFFECT REDUCTION IN CROSS-SECTIONAL AREA WHILE THE STEEL IS HEATED TO A TEMPERATURE ABOVE 450* F. BUT BELOW 600* F. WHEREBY PHYSICAL AND MECHANICAL PROPERTIES OF THE STEEL ARE IMPROVED. 